Thyrotropin (TSH) in mouse thyrotropic tumor cells is glycosylated through a dolichol lipid-linked oligosaccharide containing 3 glucoses, 9 mannoses and 2 N-acetylglucosamines. The first Alpha glucoses on subunits are rapidly removed within 10 minutes but the third is removed more slowly. Subsequently over the next two hours, the last glucose and 6 of the 9 mannoses are removed and additional sugars added to produce complex oligosaccharides; Beta is processed more rapidly than Alpha. Subcellular fractionation studies indicate that the initial steps in carbohydrate processing occur in the rough endoplasmic reticulum, but the late addition of sugars occurs in the Golgi and post-Golgi compartments.